: The overall goal of the investigator's laboratory centers on how the architecture of the mammalian nucleus influences the control of gene expression. RNA processing reactions form a vital link in the pathway of gene expression, and small nuclear ribonucleoproteins (snRNPs) have been shown to play key roles in RNA processing reactions. Ribonucleoproteins are frequent targets for autoimmune responses in rheumatic disorders such as lupus erythematosus, scleroderma and Sjogren's syndrome. Since understanding the organization and nuclear "zip-coding" of genes and their products in vivo requires techniques which can visualize whole cells, they have chosen to use fluorescence in situ hybridization (FISH) and digital imaging microscopy to study the intracellular distribution of ribonucleoproteins (RNPs) and chromatin (DNA). In contrast with the progress that has been made in analyzing the RNA processing machinery in vitro, relatively little is known about how these factors are organized in vivo or how processing is integrated with transcription, poladenylation and transport. RNPs play vital roles in cell biology. By defining the intracellular locations of these complexes relative to other subcellular components or landmarks, the investigator's will gain insights into the cellular processes in which RNPs participate. The two specific aims of the proposal are: (1) To identify chromosomal loci that colocalize with coiled bodies in mammalian cell nuclei and to understand the nature of these associations. Coiled bodies (CBs) are nuclear organelles of unknown function in which elements (mainly RNPs) of three major RNA processing pathways accumulate: pre-mRNA, histone mRNA and rRNA processing. In addition, they have found that CBs are frequently associated with the gene clusters that encode the histone, U1 and U2 RNAs in interphase HeLa cells. Experiments are proposed to identify the nature of these associations. (2) To characterize the structural composition and molecular physiology of a previously unidentified nuclear subdomain. Two classes of small polymerase III RNAs, including the Ro RNAs, concentrate within this novel structure we call the perinucleolar compartment (PNC). As part of this aim, he will determine the subcellular location of Ro RNPs, identify other components which may colocalize in PNCs and investigate the possibility that RNPs within the PNC may shuttle between the nucleus and the cytoplasm. The investigator's are in an outstanding position in terms of timeliness and expertise to study the subcellular organization of RNPs within these fascinating nuclear subdomains and to correlate their distributions with those of specific chromosomal sequences. Together, these studies should lead to new and interesting insights into the functional organization of the mammalian nucleus.